ESTRO 2023 - Abstract Book

S1220

Digital Posters

ESTRO 2023

In the experimental arm men are prescribed 24Gy in 2 fractions with a GTV boost of 27Gy. The dose constraints are shown in Table 1.

To promote patient comfort and dose precision each fraction in the 2-fraction arm is delivered in two sub-fractions, delivered sequentially on the same day,

On the day of treatment, the plan is matched to the patient’s position on the Session MRI. The plan is recontoured online using the adapt-to-shape workflow to account for any anatomical changes. A verification MRI is then acquired, and any further deviations in the position prostate accounted for with adapt-to-position prior to treatment delivery.

After sub-fraction 1 the patient gets off the couch to pass urine and waits 15 minutes for bladder filling before getting back on the couch for sub-fraction 2.

We aimed to establish if the plans prescribed for the patients receiving 4 sub-fractions were meeting the clinical goals set out in the protocol.

Materials and Methods 20 patients have now been treated within HERMES with 10 patients receiving 2 fraction SBRT.

We reviewed the plans prescribed for each sub-fraction. A total of 40 plans were evaluated from the 10 patients treated with 2 fraction SBRT.

The percentage of all sub-fractions that met the optimal and mandatory dose constraints were calculated.

Results All 40 sub-fractions treatments were delivered without delay and were well tolerated by patients.

The optimal dose constraint was met in 74% of all cases, where applicable. The mandatory dose constraint was met in 97% of cases across all 40 sub-fractions. The urethral D10% <2600cGy (+100cGy) was exceeded once, the PTVpsv_2400-GTVpb_2700 in 3 sub-fractions and the rectal V2080cGy < 1 cm3 in 6 sub-fractions (all values taken to 2 decimal places).

Conclusion